Abstract

An investigation was undertaken on two Nostoc strains isolated from the paddy fields of Iran and having different morphologies of polysaccharide sheaths. Extracellular polysaccharides (EPS) presumably play a major (protective) role in cyanobacteria but there are no clear reports
that link EPS production with (selected) abiotic stresses. The aim here is to investigate key factors enhancing EPS biosynthesis. The relationship between cell growth and the amount of EPS were compared under photoautotrophic, mixotrophic and heterotrophic growth conditions as well as
under different salt concentrations, and under nitrogen-deplete and nitrogen-replete conditions Cell growth and EPS production are both highly dependent on culture conditions, but there is no correlation between cell growth and EPS production in cultures grown in different sources of nitrogen.
In contrast, light intensity and cell growth in cultures experiencing mixotrophic conditions at either 150 or 50 μmol photon m–2 s–1 have strong positive effect on EPS production. In salt-rich cultures, in the ASN_S strain the outer cell layers protect
the inner cells from NaCl s tress and hence its growth is maintained without inhibition under the NaCl stress. Each strain of Nostoc exhibits a different pattern of EPS synthesis, making it essential that the optimal culture conditions are determined for each species reading to
the development of an efficient technology for the maximum production of cyanobacterial EPS.